The overall purpose of this study is to improve our understanding of normal and arrested differentiation in precursors of the B-lymphocyte line. In the initial phase, our investigation will focus on maturation arrests in lymphoblastic leukemic cells of pre-B type, since they are accessible from patients that comprise the most prevalent clinical manifestation of this developmental defect. Studies on lymphoid malignancies will subsequently be extended to normal B-lymphocyte precursors and to the arrested pre-B cells in patients with X-linked agammaglobulinemia (X-LA). Using immunofluorescence methods to detect surface antigens, surface immunoglobulin (Ig) and cytoplasmic Ig, we will precisely define the level of developmental arrest in leukemic pre-B cells and the portion of cells demonstrating such blocks within a given leukemic population. Using newly developed soft agar and methyl cellulose cloning assays, we will separate heterogeneous groups of leukemic cells into uniform subclones for comparative studies. We will determine the characteristics of Ig chains expressed in pre-B leukemic cells, since Ig type and location represents the major recognizable distinction between pre-B cells and their progeny. We will attempt to induce differentiation of pre-B and "null" leukemic cells by using conventional stimulants, EB virus, monoclonal antibodies and somatic cell hybridization. The results of these studies will indicate the potential of these cells to bypass their developmental block. Detailed examination of the Ig molecules produced by stimulated pre-B cells may clarify the role of pre-B cells in the generation of antibody diversity. This study should contribute substantially to knowledge of mechanisms governing the differentiation of B-lymphocyte precursors. It will provide insight into the cause of impaired differentiation in pre-B and "null" cell leukemias, which together comprise the majority of childhood leukemias, and in X-LA. Induction experiments may suggest agents of potential therapeutic value in circumventing the maturation arrests in these cells. Basic mechanisms of cellular differentiation, proliferation and Ig synthesis revealed in this study may have broader application to other defects in normal development.